function show (id, len) {

  if (document.getElementById('img_0'+id)) {
    
    for (var i=1; i<=len; i++) {
      
      if (i == 1 && id == 1) document.getElementById("buttonbefore").disabled = true;
      if (i != 1 && id != 1) document.getElementById("buttonbefore").disabled = false;
      if (i == len && id == len) document.getElementById("buttonnext").disabled = true;
      else document.getElementById("buttonnext").disabled = false;
      
      if (document.getElementById('img_0'+i)) document.getElementById('img_0'+i).style.border = '2px solid white';
    
    }
    
    document.getElementById('img_0'+id).style.border = '2px solid rgb(212, 179, 89)';
    document.getElementById('imagenr').innerHTML = 'Bild ' + id + '/' + len;
  
  }
  
}

function next (len) {
  
  for (var i=1; i<=len; i++) {
    if (document.getElementById("img_0"+i).style.border == '2px solid rgb(212, 179, 89)' || document.getElementById("img_0"+i).style.border == 'rgb(212,179,89) 2px solid') {
      show(i+1, len);
      break;
    }
  }
  
}

function before (len) {
  
  for (var i=1; i<=len; i++) {
    if (document.getElementById("img_0"+i).style.border == '2px solid rgb(212, 179, 89)' || document.getElementById("img_0"+i).style.border == 'rgb(212,179,89) 2px solid') {
      show(i-1, len);
      break;
    }
  }
  
}